1. Field of the Invention
The invention relates to the coupling of R.F. waveguide, particularly with respect to coupling and uncoupling a movable R.F. waveguide with respect to a fixed waveguide.
2. Description of the Prior Art
Rigid waveguide, flexible waveguide and rotary microwave joints are commonly utilized to configure microwave transmission systems. Such components include flanges which are bolted together to provide appropriately aligned R.F. paths with zero air gaps. Rotary waveguides are utilized when portions of systems rotate with respect to each other. Flexible waveguide is utilized when one portion of a system experiences small amplitude translational motion with respect to another portion of the system. In commonly encountered situations, the relative motion is often of a magnitude that flexible waveguide cannot practically and reliably accommodate the displacements. In such arrangements, the R.F. path is coupled and uncoupled by waveguide flanges that are positioned as close as possible with respect to each other, without mechanical coupling therebetween, so that the coupling and uncoupling required by the relative motion can occur. This arrangement is, for example, utilized in rotatable radar antenna mast configurations where the mast is extended and retracted over relatively large distances.
Such a system is disclosed in pending U.S. patent application Ser. No. 07/618,782 entitled "Mast Translation And Rotation Drive System Utilizing A Ball Drive Screw And Nut Assembly" by William E. West and assigned to the assignee of the present invention. In the system of said Ser. No. 618,782, a radar antenna is extended from a submarine, rotated in a scanning mode and retracted back into the submarine when not in use. A rotary joint attached to the antenna mast accommodates the rotational motion but travels through large linear displacements during extension and retraction. In the prior art, the rotary joint waveguide flange is not physically coupled to the flange of the stationary rigid waveguide that provides the R.F. signal to the antenna when the mast is extended. The two waveguide flanges are positioned as close as possible with respect to each other so as to accommodate the relative translational motion during extension and retraction. This arrangement results in an air gap and waveguide misalignment that vary as the antenna rotates. The air gap and misalignment result in system R.F. losses, signal fluctuations and safety hazards. In order for reasonable R.F. coupling to be maintained, this prior art arrangement requires position accuracy and repeatability each time the antenna is raised.